This invention relates generally to a planar xe2x80x9cfacexe2x80x9d type carbon segment commutator assembly and a method of securing carbon commutator segments to a metallic conductor to make such an assembly.
It is known for a planar carbon segment commutator to include metallic conductor sections supported in a circumferentially spaced array around an annular front surface of an annular hub comprising an insulating material. It is also known for such a commutator to include carbon commutator segments that are formed around and interlocked with portions of the respective metallic conductor sections. The carbon commutator segments define a flat composite commutating surface. An example of such a commutator is disclosed in U.S. Pat. No. 5,912,523, which issued Jun. 15, 1999 to Ziegler et al., is assigned to the assignee of the present invention and is incorporated herein by reference. To positively locate and secure the carbon segments they are embedded in the hub.
In addition, U.S. Pat. No. 5,925,962 issued Jul. 20, 1999 to Kobman et al. and the Ziegler patent both disclose overmolding carbon and insulator material onto a metallic substrate in the manufacturing process and pressing the overmolded carbon compound through holes in the metallic conductor sections to effect a more secure mechanical interlock between carbon segments and conductor sections.
What is needed is a planar commutator segment attachment assembly that supports and positively secures carbon commutator segments without overmolding hub material around the carbon segments or otherwise directly connecting the carbon segments to the hub. What is also needed is a more simple and inexpensive method of installing carbon segments in a commutator manufacturing process.
A planar commutator assembly is provided that includes an annular hub comprising electrical insulating material and a plurality of metallic conductor sections supported in an annular circumferentially-spaced array on the hub, each conductor section including a first front projection integrally extending from a front surface of each conductor section. The planar commutator assembly also includes a plurality of carbon commutator segments disposed on respective ones of the conductor sections and defining a flat composite annular front commutating surface. The front projections are disposed in cavities in corresponding commutator segments.
The first front projection of each conductor section has a first cross-section parallel to and adjacent the back surface of a corresponding commutator segment and a second cross-section parallel to and spaced axially forward of the first cross-section. The second cross-section has a greater area that the first cross-section to prevent withdrawal of the first front projection of each conductor section from its corresponding commutator segment. The first front projection of each conductor section mechanically locks one of the commutator segments to the conductor section. The first front projections provide positive mechanical locks that obviate the need to further secure the commutator segments by such means as partially embedding them in the hub.
The invention also includes a method for making a planar commutator that includes forming an annular conductor substrate including a first circular front projection that extends integrally and axially from a front surface of the substrate. An annular carbon disk is formed on the conductor substrate by overmolding a carbon compound onto the front surface of the conductor substrate and around the first circular front projection. The compound is then allowed to harden. An annular hub comprising an insulating material is then provided and the conductor substrate is connected to a front surface of the hub. Electrically isolated, circumferentially-spaced commutator segments and corresponding mechanically interlocked conductor sections are then formed by providing radial cuts through the annular carbon disk and the metal substrate, respectively.